The “PHP Warning: Constant ABSPATH already defined in wp-config.php” error message occurs when the ABSPATH constant is defined more than once in the wp-config.php file.
The ABSPATH constant is used to define the absolute path of the WordPress installation on the server. It is defined in the wp-config.php file, and should only be defined once. When it is defined more than once, this generates a PHP warning.
To resolve this issue, you will need to edit the wp-config.php file and remove the duplicate definition of the ABSPATH constant. The ABSPATH constant is typically defined at the top of the wp-config.php file, so you should be able to find it easily. Once you’ve located the duplicate definition, remove it and save the file.
Here is an example of what the ABSPATH constant looks like:
define('ABSPATH', dirname(__FILE__) . '/');
After removing the duplicate, you should also check if there’s any other constants that are defined multiple times in the wp-config.php file, and remove the duplicates.
Please note that before making any changes, it’s recommended to have a backup plan in case something goes wrong, and also to test the changes before applying them to your production environment.